need help figuring buoyancy

[bowfishin fool]

i am biulding small pontoons for the side of a jon boat, so i can put a bigger deck on. does anyone know how to figure out how big my pontoon has to be(volume) to hold a certain amount of weight??

thanx

reed

[Brannon74]

I don't, but take pics as you do it and post it in the DIY please.

[Texastaxi]

The weight of the volume that the pontoon displaces must be greater than the weight it's going to support.

A simple example. If you're going to float 10 lbs, you need to be able to displace 1.25 gallons of water. Water weight approximately 8.2 lbs/gallon.

For a safety factor, you might want to go 2.5 to 3 gallons of pontoon per 10 lbs of weight. To double check the safety factor of the entire boat, you could divide the weight of the boat by the volume of the existing pontoons.

That's the simplest description I can give you.

[Big Brass]

I may be wrong on this but if I remember correctly:

Take the weight you want the pontoon to support.

Water weighs 8.34 lbs/gallon.

Divide the weight you want the pontoon to support by 8.34 lbs/gallon to give the volume, in gallons, of water you need to displace to support that amount of weight.

Divide this number by 7.48 (the number of gallons in a cubic foot) to give the cubic foot size pontoon you will need to support the weight.

Example:

I weigh 280 lbs.
280 divided by 8.34 lbs/gallon = 33.57 gallons
33.57 gallons divided by 7.48 gallons/cubic foot = 4.49 cubic feet
It will take a pontoon with a volume of 4.5 cubic feet to support my weight.

I would add in a certain amount of safety factor above what you calculate when building the pontoon.